This invention relates to acoustic imaging arrays.
It is well known to use a row of acoustic elements in an acoustic imaging system. These are in the form of a one-dimensional (1D) array such as a series of individual elements spaced along a single row or column. Conventionally the acoustic elements are formed from a piezoelectric material. The elements generate an acoustic signal which propagates through a medium and is reflected by an object in the medium which is to be detected. Signals reflected by the object are detected by the elements and electrical signals are generated which can then be processed. An acoustic imaging system using a 1D array is used in ultrasound imaging to provide internal images of the human body or to image underwater objects. A two-dimensional (2D) image is generated by physically sweeping the 1D array over the region to be imaged.
It has been proposed to use 2D arrays to generate 2D and 3D images. A 2D array may be a plurality of individual elements arranged in a grid. Compared with a 1D array, a 2D array provides improved resolution and better quality image and also eliminates the need for physical focussing or sweeping allowing real time images to be obtained. However, the use of 2D arrays has been limited by the difficulty in processing large amounts of data which would be generated by an array of any useful size, for example 10,000 elements in an array of 100.times.100. Furthermore, it is difficult to make connections to such a large number of elements on a scale of several centrimeters squared.
Although the difficulties in data processing can now be tacked by using high power computers having faster processing speeds it does not deal with the problem of the large number of connections. The connections and associated connecting tracks are supported by an interconnect layer. However, the interconnect layer often has an acoustic impedance which differs to that of the elements and acoustic reflections are caused by the mismatch. Although reflections can be minimized using materials having a better match of acoustic impedance, problems are encountered as the number of elements in an array is increased. As the number of elements in the array increases the thickness of the interconnect layer must also be increased which increases the amount of acoustic reflections. This degrades the sensitivity of the system.
Another problem is cross coupling between elements in the array. This becomes more severe as the scale of the array is reduced and the elements are closer together.